PAULSBORO, N.J. — A freight train derailed Friday on a railroad bridge that has had problems before, toppling tanker cars partially into a creek and causing a leak of hazardous gas that was blamed for sickening dozens of people, authorities said.

Members of the National Transportation Safety Board arrived in New Jersey on Friday afternoon to investigate.

The accident happened just after 7 a.m. when a train with two locomotives, 83 freight cars, and a caboose made its way from Camden to the industrial town of Paulsboro, just across the river from Philadelphia International Airport.

Cars from a train operated by CSX went off the rails on a swing-style bridge, owned by Conrail, over Mantua Creek.

Seven cars derailed, including two box cars on stable ground and five on the bridge. Deborah Hersman, board chairwoman, said four tankers were partially in the creek.

One tanker containing 25,000 gallons of vinyl chloride was sliced open in the accident and some of the gas spewed into the air, while the rest turned into a solid and settled into the bottom of the tanker.

People who live nearby said the air was smoky in the morning. Doug Ricotta was working in his bakery when he heard a loud sound. ‘‘Next came a smell, kind of sweet — not a healthy smell,’’ he said. He stayed in his business and kept baking, though one catering order had to be canceled because roads into and out of town were closed for a few hours.

Breathing vinyl chloride, which is used to make the common plastic PVC, can make people dizzy or sleepy. Breathing very high levels can cause someone to pass out, and breathing extremely high levels can cause death.